perf: fast-path canonical grain manifests

Avoid re-deduplicating grain manifests which are already known canonical while preserving the fallback for equivalent unseen manifests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ReubenBond

src/Orleans.Core.Abstractions/Manifest/ClusterManifest.cs

@@ -102,12 +102,17 @@ private static (ImmutableDictionary<SiloAddress, GrainManifest> Silos, Immutable
 
             GrainManifest GetCanonicalManifest(GrainManifest manifest)
             {
-                manifest = DeduplicateManifest(manifest);
                 if (canonicalManifests.TryGetValue(manifest, out var canonicalManifest))
                 {
                     return canonicalManifest;
                 }
 
+                manifest = DeduplicateManifest(manifest);
+                if (canonicalManifests.TryGetValue(manifest, out canonicalManifest))
+                {
+                    return canonicalManifest;
+                }
+
                 canonicalManifests.Add(manifest, manifest);
                 uniqueManifests.Add(manifest);
                 return manifest;